GUWAHATI, India - About 2.5 million people have been made homeless in India's northeast state of Assam after a second wave of flooding caused by heavy rains over the past three days, an official said on Monday.

The flooding has affected about seven million people and killed 12 people since Friday and has washed away thousands of homes, bridges, electricity poles and telecommunications towers -- disrupting power and phone networks in many areas.

"This is the worst flood we have ever experienced. The damage caused is unbelievable," said Bhumidhar Burman, Assam's relief and rehabilitation minister.

"Right now we are concentrating on rescue operations and the army has been called to help us ... people will find no respite until the rains stop."

Since the annual monsoon rains began in June, about 50 people have been killed in Assam and more than 12 million people affected, including in the latest wave of flooding.

The second spell of flooding in less than a month has also spread across parts of Bangladesh, killing seven people, forcing half a million from their homes and leaving thousands stranded.

The worst affected were farmers who had replanted crops lost in earlier flooding.

In Assam's main city, Guwahati, several residential areas are under waist-deep waters, forcing many residents to move into hotels or into relatives' and friends' houses.

Landslides in parts of the northeast region blocked highways and stranded thousands of trucks carrying essential goods, such as food supplies.

As water levels continue to rise, villagers have moved to higher ground using boats or rafts made from bamboo and banana trees, leaving behind their belongings and livestock.

"This flood has come at a time when the people had just returned home and were rebuilding their lives after the devastation caused by the previous floods," said Utpal Dutta, a local leader in the worst-hit Lakhimpur district of Assam.

The flooding has also affected the neighbouring Himalayan kingdom of Bhutan where several fast-flowing mountain streams are changing their course, flooding human settlements.

The regional weather office in Assam predicted more rain over coming days, and authorities were air-dropping food and medicines in remote areas.

Since July, more than 2,000 people in eastern India and neighbouring Bangladesh have been killed by snake bites, drowning, diarrhoea and from houses collapsing after swollen rivers burst their banks as a result of incessant monsoon rains.